The subject matter disclosed herein relates to treating metal and, in particular, to monitoring laser metal treatments.
Laser peening, or laser shock peening (LSP), is a process of inducing beneficial residual compressive stresses into a material (usually metal) by using a powerful laser. As used herein, a material being processed shall be referred to as a “treated material.” An ablative coating, usually black tape or paint, is applied to the treated material to absorb the energy from a laser. Short energy pulses from the laser are then focused to explode the ablative coating, producing a shock wave. The process may be repeated in multiple locations. A translucent layer, usually consisting of water, is required over the coating and acts as a tamp, directing the shock wave into the treated material.
A piezoelectric sensor is normally used for real time (on-line) monitoring of LSP processing. The piezoelectric sensor converts the stress (acoustic) waves created by LSP into an electric signal proportional to the strength of the wave. The electric signal may then be used to monitor the LSP process. The piezoelectric sensor, however, is often destroyed because it is in direct contact with the treated material. The one-use destruction of these gauges requires the use of multiple gauges for wherever multiple laser pulses are needed.